Temperature Fluctuations And Reloading Brass- Part 1

In the old days of reloading brass, temperature fluctuations caused a great deal of issues on the powder charge, causing extreme differences in the way the ammo performed. This was due to the amount of cordite in the powder. Post WW2, modern powders began using less cordite, supposedly removing the effects of temperature changes. That begs the question; does extreme hot or cold effect reloading brass performance?

There was a time in late July where I lined up a shot at 400 yards, using a round I had created 6 months prior. Sure, that my target was on the crosshairs, I fired. Much to my surprise, I missed. Not only that. When I went to eject the fired casing, smoke bellowed out and a lose primer fell from the base of the reloading brass. In the late July heat, it hit me; I had created that round in the dead of winter.

Heat can not only turn apparently safe handloads into dangerously hot handloads, but — legend has it — it also affects velocities and can cause shots to go awry.

Some gunpowder has the reputation of being particularly susceptible to variations in temperature. Alliant’s Reloder line is one, for example. Others, such as Hodgdon’s Extreme line, are purposely designed to be stable in extremes of heat and cold.

Trouble is, many propellants with a reputation for instability in extreme temperatures are very good powders that make assembling accurate hand loads easy. Reloder 22, for instance, is my all-time favorite powder for magnum rifle cartridges because it is quite easy to get it to shoot well.

The question we’re tackling here is threefold:1. Is gunpowder sensitive to temperature swings?2. Are some propellants more temperature sensitive than others?3. If so, are the velocity variations caused by extremes in temperature enough to change point of impact at hunting ranges and cause a miss on an animal?

First, let’s establish what “hunting ranges” means. Most hunters have no business shooting at game past 300 yards, but we’ll give ourselves the benefit of the doubt and make 400 yards the outside parameter of our standard, common, hunting-range category.

But what about all the long-range shooters out there now that consider connecting on a deer at very long distances to be the greatest “trophy” of the hunt? To them, 400 yards is close. So, if temperature-induced velocity variation does indeed occur, let’s also examine the effect on point of impact at 800 yards — double our typical “long” distance.

To test whether temperature-induced velocity anomalies are fact or fiction, I loaded 10 rounds each for the 7mm Remington Magnum, a popular long-range hunting cartridge. I used Nosler’s 160-grain AccuBond and two propellants, Hodgdon’s H-1000 — which has a reputation for stability in temperature extremes — and my old standby, Reloder 22 — which has a reputation for volatility in temperature extremes.

Each batch was loaded with charge weights near maximum but previously proved to be safe in that particular rifle.

Half of each batch I put in the freezer overnight. The next morning, I set the ammo box on the dash of my truck and let it sit in the August sun until after lunch, by which point the interior of my pickup was stiflingly hot. Thus prepared, I loaded up my chronograph and rifle, put the frozen ammunition in a small cooler with several ice packs and headed to the range.

Ideally, I’d have frozen the rifle between each cold-round shot, but, unfortunately, the range doesn’t have a deep freeze, and I wouldn’t have had time if it had. To minimize the effect of a warm chamber, I attempted to send each shot through the chronograph screens within three to five seconds after dunking the cartridge into the action. I also allowed the rifle to cool — as much as it would on a 95-degree day — between five-shot strings.

For the results of our little experiments, be sure to read part two of this series on temperature variations.